A multilayer wiring structure of a semiconductor device is formed by embedding a metal wiring in an interlayer insulating film. As a material of the metal wiring, copper (Cu) is used because of its small electro-migration and its small low resistance. A damascene method is generally used for forming the multilayer wiring structure. In particular, a dual damascene method is an advantageous method having lesser steps. In the dual damascene method, Cu is simultaneously embedded into a connection hole and a wiring groove which have been previously formed in an interlayer insulating film.
In the dual damascene method, a trench in which a wiring is arranged in a layer, and a via hole for connecting an upper wiring and a lower wiring, are formed in an interlayer insulating film of a substrate. Then, Cu is embedded into these recesses by a CVD method or an electroplating method. Before each of these recesses is embedded with copper, a Cu seed layer serving as an electrode may be formed along an inside surface of the recess, in order for a suitable embedment of Cu. In addition, since Cu tends to diffuse in the interlayer insulating film, it is necessary to form a barrier layer, which is formed of e.g., a Ta/TaN laminate body, in the recess. Thus, a barrier layer is sometimes formed on the surface of the interlayer insulating film and the inside surface of each recess by a sputtering method, for example, and a Cu seed layer is further formed thereon.
In recent years, as a method for forming a barrier layer, the following method has been regarded as favorable (for example, JP2007-221103A). Namely, a seed layer made of CuMn alloy is formed by sputtering on a recess formed in an interlayer insulating film formed of a SiO2 film or a SiOCH film that is a low dielectric constant film. Then, Mn atoms in the CuMn alloy and oxygen (O) atoms in the interlayer insulating film are reacted with each other, so that a barrier layer made of manganese oxide is self-formed on the surface of the interlayer insulating film.
As compared with the method of forming a barrier layer of a Ta/TaN laminate body, the above method is advantageous in that a barrier layer sandwiched between the interlayer insulating film and a Cu wiring can be made thinner. However, in the method of forming a CuMn-alloy seed layer by a sputtering method, an inside surface of a small recess cannot be well coated, so that the inside surface cannot be well coated with Mn. Thus, Cu diffuses in the interlayer insulating film, which impairs an insulation property of the interlayer insulating film.
Thus, in order to improve a coating property of a barrier layer in the recess, the present inventors have developed a method of forming a barrier layer in which a gas containing an organic compound of manganese is supplied, so as to directly form a barrier layer made of the manganese compound inside the recess formed in an interlayer insulating film. To be specific, a steam of an organic compound of manganese is reacted with oxygen, carbon, or silicon, which is one of the components contained in the interlayer insulating film, so as to form a barrier layer made of the manganese compound inside the recess. Alternatively, a steam of an organic compound of manganese is reacted with an oxygen gas, so as to form a barrier layer made of manganese oxide. However, these methods have the following problems. Namely, after a barrier layer has been formed by these methods, and a Cu seed layer has been formed thereon, a Cu wiring is formed in the recess. In this case, since the barrier layer and the Cu wiring with the Cu seed layer therebetween do not well adhere to each other, the Cu wiring formed in the recess may peel therefrom. Thus, the wiring may be damaged to invite breaking of the wire. In addition, also in a case where the Cu wiring is directly formed on the barrier layer, since the barrier layer does not well adhere to the Cu wiring, the same problem may arise.
In addition, there is another problem. Namely, when a barrier layer is formed, excessive manganese, which did not react with the part of the components contained in the interlayer insulating film or the oxygen gas, may be drawn (taken) into the surface of the barrier layer or into the barrier layer, so that the excessive manganese may diffuse in the Cu wiring. In this case, since electric conductivity of Mn is significantly lower than that of Cu, electric resistance of the Cu wiring may undesirably increase.